South Korea and China are the nations most at risk should conflict break out on the Korean peninsula. It is in their interests that they have good relations so they can coordinate a strategy to ensure North Korea and the United States do not come to blows. Yet celebrations last week of the 25th anniversary of ties were low-key, reflecting how bad the relationship has sunk over Seoul’s decision to push ahead with a US missile shield system that Beijing claims has intrusive spying capabilities. The South should break from the constraints it has created for itself and play a more constructive role.

Proving how ties have soured, there was no joint celebration like that held in 2012 to mark the 20th anniversary. Then, senior officials attended celebratory events in Beijing and Seoul. Last Thursday, though, presidents Xi Jinping and Moon Jae-in and their foreign ministers merely exchanged conciliatory messages, the former calling for a fair settlement of differences and the latter being hopeful of a meaningful strategic partnership.

Unmentioned, but alluded to by Xi, was the US Terminal High Altitude Area Defence (THAAD) missile interceptor system deployed by Seoul despite objections from Beijing. Moon gave hope that the system would not be deployed when he took office in May. He knew only too well how it was harming his country’s ties with China, with tourism and trade having been badly hit. The former Korean war adversaries had forged strong economic cooperation and understanding was being built through tourism and student exchanges.

But regular missile tests by North Korea, such as that launched over Japan on Tuesday, have prompted Moon to backtrack on a suggestion that he would order a freeze in the deployment of THAAD. That is despite Beijing and Moscow claiming the system can spy deep into their territory and weapons experts saying it will be ineffective should the North fire multiple rockets at the same time. But South Korea’s alliance with the US, it hosts 28,500 American troops, has also long been problematic and the THAAD decision only confirms the belief that Seoul is being used by Washington to push its agenda.

Moon has reached out to the North for peace talks and this is the approach the US, as the great rival of Pyongyang, should adopt. A military solution like that hinted at by US President Donald Trump is not an option. But South Korea has also become a leading economic and industrial power and it should step out of Washington’s shadow.

The THAAD issue and even threats by North Korea could be better dealt with were Seoul to take a more resolute role in regional diplomacy.